| 摘要 |
PURPOSE:To mold a highly accurate plastic lens in a shortened molding cycle by a method wherein the diametral dimensions of the part, which connects to a gate and is on the gate side, of a runner are specified. CONSTITUTION:The gate side part 26 of a runner has a diameter, which is 1.3 times as large as the average thickness between the thickness at the intermediate diameter of a cavity 20 and that at its outer diameter, and a length, which is almost equal to the outer diameter of the cavity 20. The reason why said length is determined is as follows: the amount of resin flowing in the cavity 20 at dwell stage corresponds to the amount developed by the shrinkage of resin in the cavity 20 due to cooling and said amount can be fully replenished by the amount of resin in the gate side part 26 having said length. The volume of the high temperature molten resin, which is filled from a molder to the cavity 20, shrinks by being cooled. The volumetric shrinkage is compensated by the influx of the amount of resin, which is responsible to the volumetric shrinkage of resin, through a gate 27. Since the cooling speed of the resin in the gate side part 26 of the runner is made to be equal to the cooling speed near the gate 27 in the cavity 20, the temperature of inflowing resin can be equal to the temperature of the respective peripheral directional part in the cavity 20, resulting in allowing to shorten molding time. |
